Chop up olives, giardiniera, pepperoncinis, capers, peppers and garlic very finely. A food processor would probably be helpful to ensure a minced texture, though be careful to not puree the mixture; you don't want a paste. If you do use a food processor, make sure to do the garlic separately to ensure that it is thoroughly and very finely minced - large pieces of raw garlic aren't very palatable.
Add in oregano (or a pinch of Italian seasoning mix), lemon zest and juice. Mix thoroughly.
Taste the mix, and add pepper if needed. At this point, you can also play with the amount of other ingredients to suit your preferences. I sometimes like a few extra green olives; my partner likes the sweetness added by the roasted peppers better.
Now the hard part: cover and refrigerate overnight to let the flavors marry. Or not -- I find it hard to plan my cravings ahead, and it's a tasty mix even the first day, though it does get better as it sits.
For a Muffaleta Sandwich: Cut a loaf of Italian (or French) crusty bread in half horizontally and remove some of the soft inside to make room for the fillings. Slather the olive salad on both sides of the bread, maybe with a quick drizzle of a good finishing olive oil, if you like. Layer on: thinly sliced salami, provolone cheese, ham, and mozzarella cheese -- Though it's not traditional, turkey or chicken are also delicious on the sandwich. (During my vegetarian years, I also liked to just use the cheeses, thinly sliced onion, tomato, avocado and sprouts.) Put the top on the sandwich and wrap the whole thing up tightly in saran wrap or butcher's paper. Try to let the sandwich sit for an hour or so in the fridge to let the olive salad soak into the bread. Cut the sandwich into pieces and serve; enjoy!
A few other ideas for using Muffaleta Style Olive Salad: Butterfly chicken breasts and use the olive salad and a slice of provolone cheese as a filling. Toss hot pasta with some of the salad, feta cheese and baby spinach. Make crostini (small slices of toasted baguette) topped with the olive salad, a bit of basil and a slice of salami for an appetizer. Mix the salad with light cream cheese and use as a sandwich/bagel spread. Put a dollop of the salad on top of a bowl of tomato-veggie soup before serving.